Texture baking noise reduction with filmic-blender, clamping does not work?
Applying simple 2D image filters for lightmap textures does not work for many reasons, primarily because it will ignore things like adjacent faces, edges, difference of shapes between faces, and other features of the 3D mesh.

But you can use the Batch Bake Blender Addon, it can use a texture noise reduction ("denoising") solution that consider the mesh geometry of the texture:



It's available at
https://noevu.com/#batch-bake

Blender Artists post: https://blenderartists.org/forum/showthread.php?443843